The HS10, HS20, HS25 and HS30 all shared the same lens assembly. But they differed in sensor sizes:

HS10 was equipped with 1/2.3" sensor

the other ones came with 1/2" sensor.

For this reason - while the real FL range stayed the same (at 4.2-126mm) - the EFL of HS10 was 24-720, but the EFL of the other models stands at 23-690.

Maybe Fujifilm reasoned that admitting the tele EFL has shrunk might hurt their market standing. So they marketed the HS20 and later models as 1/2" & 720mm camera.

It is telling that Fujifilm was quick to announce the opposite EFL change (from 400mm to 436mm) with S100fs -> S200EXR transition, which involved the sensor size change (at that time a shrinkage) while retaining the lens assembly.